Method of manufacturing magnet cores and magnet cores manufactured by the same

ABSTRACT

The invention relates to a method of manufacturing magnet cores consisting of representatives of a special class of lithium-, copper-, zinc-, (cobalt-) ferrites, by sintering at temperatures which do not exceed 1100*C. These cores may serve to replace, nickel-containing and hence more expensive, ferrite cores which may serve as &#39;&#39;&#39;&#39;yoke&#39;&#39;&#39;&#39; rings or as aerial rods.

United States Patent 1191 1 51 Jan. 9, 1973 221' Filed:

Ritzen et al [54] METHOD OF MANUFACTURING MAGNET CORES AND MAGNET CORES MANUFACTURED BY THE SAME v [75] Inventors: Johannes Maria Jozef Ritzen; Hans Peter Peloschek, both of Emmasingel, Eindhoven, Netherlands [73] Assignee: U.S. Philips Corporation, New

York,N.Y.

June 24,1971

21 Appl. No.: 156,573

[30] Foreign Application Priority Data June26, 1970 Netherlands 700942l [52] US. Cl. ..252/62.6, 252/6261, 252/6262 [51] Int. Cl. ..C04b 35/26 [58] Field of Search .L...252/62.6l, 62.6, 62.62

[56] I I References Cited UNITED STATES PATENTS 2,751,353 '6/1956" Gorter ..252/62.61

Primary Examiner-James E. Poer Assistant Examiner-J. Cooper Attorney-Frank R. Trifari 71 ABSTRACT The invention relates to a method of manufacturing magnet cores consisting of representatives of a'special class of lithium-, copper-, zinc-, (cobalt-) ferrites, by sintering at temperatures which do not exceed 1 100C. These cores may serve to replace, nickel-containing and hence more expensive, ferrite cores which may serve as yoke rings or as aerial rods.

6 Claims, No Drawings METHOD OF MANUFACTURING MAGNET CORES AND MAGNET CORES MANUFACTURED BY THE SAME e. TF (in temperature range from 5 C to 55 C, having 23 C as the reference temperature) X 10'.

The temperature factor (TF) is the most reliable The invention relates to a method of manufacturing 5 tandard for the temperature dependence of the magmagnet cores consisting of a soft magnetic ferrite and to ferrite cores manufactured by this method.

Magnet cores which consist of a soft-magnetic ferrite and which on the one hand satisfy three quality require ments to be defined in detail below and which on the other hand are distinguished by comparatively low manufacturing costs formed the object of the examination which has resulted in the present invention.

The said quality requirements are:

a. the initial permeability (m), measured at a temperature of 23 C and a frequency of 4 kHz, is higher than 150;

b. the specific resistivity (p), measured at a temperature of 23 C, is higher than 10 ohm cm;

c. the Curie temperature (T is higher than I30 C; the Curie temperature is to be understood to mean herein that value of the temperature at which the initial permeability, as a function of the temperature, after having reached its maximum value has fallen with increasing temperature to a value of 10 percent of the said maximum value.

The requirement of comparatively low manufacturing costs implies that the magnet cores in question may not contain nickel and that they can be manufactured by means of a sintering process which requires no temperatures higher than i 100C and which can be carried out in air.

It was far from easy to manufacture magnet cores in which all the said requirements which mutually are more or less conflicting can be satisfied simultaneously. For example, although magnet cores consisting of manganese-zinc-ferro-ferrite are distinguished by a comparatively high initial permeability, they show a comparatively low specific resistivity, in the order of magnitude of 10 ohm.cm, while the sintering temperatures required for the manufacture of said magnet cores are rather high, namely from 1200 "C to 1350 C. The possibility of realizing soft-magnetic ferrites while using comparatively low sintering temperatures with on the one hand a comparatively high initial permeability and on the other hand a comparatively high resistivity is present, it is true, but one is committed to nickel-zinccopper ferrites which are comparatively expensive in connection with the nickel present therein. During the preparation of said ferrite, the sintering should often be carried out in an atmosphere which is rich in oxygen.

The invention is particularly suitable for the preparation of so-called yoke rings" and aerial rods.

Yoke rings" are to be understood to mean magnet cores consisting of soft-magnetic ferrite and to be used at frequencies varying from 4 to 1000 kHz in deflection coils for television display tubes. Besides the abovementioned quality requirements b and c, said yoke rings must preferably also satisfy the requirement that the initial permeability should be higher than 300 (a, 300).

Aerial rods to be used at frequencies higher than 1 MHz must satisfy, besides the above-mentioned quality requirements a, b and c, preferably also the following quality requirements:

d. lg 8m, (at a temperature of 23 C and a frequency of 1.5 MHz) 70 X 10 netic initial permeability of the magnet core. It is defined as follows:

wherein (m), is the value of the magnetic initial permeability of the magnet core in question at the temperature t while 1 is the value of the magnetic initial permeability at the reference temperature t,.. As a rule, and in this case also, room temperature (23 C) is chosen for the reference temperature t,.

The magnet cores manufactured according to the invention consists of soft-magnetic ferrites built up from ferric oxide,Fe2O3, copper oxide, CuO, lithium oxide LizO, zinc oxide, ZrO, and, possibly, cobalt oxide, C00. These ferrites may be considered as mixed crystal materials having as mixed crystal components cubic ferrite CuO, FeOa, zinc ferrite, zn'o-rezoa, possibly cobalt ferrite, CoO, Fe2O3, and in addition the ferrite of the bivalent complex (Li0.5+Fe0.5 which fern'te thus has a composition according to the formula (Li FeO,O,=. )O-Fe2O3. This ferrite is a known material the composition of which in the technical literature is usually referred to by means of the formula LiZO-S Fe2O3(see, for example, Naturwissenschaften 26, p7 431 (i938) and Dutch Pat. specification No. 77,389) which formula is a different notation for the abovementioned formula: (Lima-LP e0 05 )O-Fe O The composition of this material in the technical literature is also sometimes referred to by the formula Li Fe 0., (see again the above-mentioned Dutch Pat. specification No. 77,389). A part of the iron oxide of the starting mixture thus takes part in the formation of the bivalent complex oxide (Li Fe )O which, like the other oxides CuO, ZnO and possibly C00, forms, with the rest of the iron oxide, a ferrite of the formula MCO'FC2BD3 (wherein Me is one of the above-mentioned bivalent metal oxides or the above-mentioned complex metal oxide). It has advantages to state the composition of the starting mixture in molecular percentages of the oxides Fe O (in as far as this does not contribute to the formation of the complex oxide of the formula (Li Fe )O, CuO, ZnO, possibly C00, and (Li Fe )O, and that for two reasons.

First of all it is found immediately in how far the composition of the starting mixture deviates from the so-called stoichiometric composition. Stoichiometric composition is to be understood to mean a composition in which the molecular percentage of the iron oxide is equal to the molecular percentage of the oxide MeO (with a single ferrite) and is equal to the sum of the molecular percentages of the oxides Me() (with a mixed ferrite), respectively, or, in other words, a composition with 50 mol.% Fe2 0 not counting iron which would cooperate in the formation of a complex bivalent oxide.

A second advantage of the above-described manner of indicating the composition of the starting mixture is related to the condition that the ratio of the molecular percentages of the complex oxide (Li Fe )0 on the one hand and the ZnO on the other hand, in the starting mixtures has been found to be of importance in relation to the magnet cores manufactured from these starting mixtures either or not fulfilling the above-mentioned quality requirements. In other words: the magnetic quality properties of the resulting magnet cores also depend upon the ratio in the starting mixture.

The method according to the invention is characterized in that a finely divided mixture of iron oxide, Fe O copper oxide, CuO, lithium oxide Li 0, Zinc oxide, ZnO, and, possibly, cobalt oxide, CoO, having a composition expressed in molecular percentages of the metal oxides, in which the lithium is deemed to be present exclusively as a component of a bivalent complex oxide having a composition according to the formula (Li Fe )O, and in which the iron which would be required for the formation of said complex bivalent oxide is not included in the notation of the quantity of iron, expressed in molecular percentages Fe O which mixture has a composition defined in this manner of:

45.0 52.5 mol of Fe O 5 20 mol ofCuO,

mol ofCoO, remainder (Li Fe )O and ZnO, in a ratio varying from 0.25 l to L5 l, is compressed in the form of the magnet core to be manufacture, after which the resulting compressed product is sintered in air or in a mixture of air and oxygen at a temperature which does not exceed 1 100 C.

As the case may be, the mixture of the above-mentioned metal oxide is prefired at a temperature of at most approximately 950 C after which the prefired product is cooled, pulverized and compressed in the form of the magnet core to be manufactured, and the resulting compressed product is sintered again in air or in a mixture of air and oxygen at a temperature which does not exceed 1 100 C.

As is know in the preparation of the ferromagnetic ferrites by sintering finely divided mixtures of metal oxides, one or more of the said oxides in the starting mixture may be replaced by another compound of the same metal, which compound can be converted into the corresponding metal oxide during the heating required for the sintering. Such compounds are, for example, carbonates, oxalates and acetates.

For the manufacture of yoke rings according to the invention start is preferably made from mixtures having a composition, defined in the same manner, of

46.5 50.5 mol of Fe O 5 20 mol ofCuO,

0 2.5 mol CoO, remainder (Li Fe )O and ZnO, in a ratio varying from 0.25: l to 0.75: i.

For the manufacture of aerial rods according to the invention, the starting material preferably are mixtures having a composition, defined in the same manner, of

47.5 50 mol of Fe o 5- mol %ofCuO,

0.7 2 mol ofCoO, remainder (Li Fe )O and ZnO, in a ratio varying from 0.25 l to l 1.

By means of the method according to the invention a number of magnet cores were prepared as follows: Starting materials were iron oxide, Fe O copper carbonate CuCO zinc oxide, ZnO, lithium carbonate, Li (O and, possibly, cobalt carbonate, Co(O The starting materials were mixed in the desired ratio. The mixture was ground in a ball mill using ethanol as a grinding liquid for 6 hours. The ground product was then filtered off, dried and prefired for one hour by heating it at a temperature of 850 C. As is known, such a prefiring is a rather universally used measure in manufacturing methods of the type in question. The prefired product was then ground for 16 hours in a ball mill using water as a grinding liquid. The ground product was then filtered off and dried. A binder was added which consisted of 2 percent solution of ammonium alginate in water. The resulting doughy mass was granulated by forcing it through the meshes of a sieve. From the granulate rings were compressed with a pressure of compression of 0.5 ton/cm? The rings were then sintered in air. For that purpose they were heated up to the peak temperature (sintering temperature) at a rate of approximately 150 C per hour. The rings were maintained at the peak temperature for approximately 15 minutes after which, again at a rate of approximately l50 C per hour, they were cooled to room temperature.

At least the first three of the following five quality values were measured in each of the resulting annular sintered bodies (magnet cores); I

l. the magnetic initial permeability, 1.1 at a frequency of4 kHz and at a temperature of 23 C;

2. the Curie temperature, T

3. the specific resistivity, p at a temperature of 23 the quotient of the loss factor and the initial permeability tgp/;t,, at a temperature of 23 C and a frequency of 1.5 MHz. 5. the temperature factor, TF, in the temperature range from 5 C to 55 C, with room temperature (23 C) as a reference point.

The compositions of the starting mixtures, the sinter ing temperatures (T used, and the measured quality values of the resulting magnet cores are recorded in the two following tables, (Tables A and B). In these tables (and also in the subsequent tables C and D) the abovementioned ratio (Li Fe )O/ZnO is briefly denoted as Li /Zn".

it is to be noted that it is also possible to heat more 1 quickly, even at a rate of approximately C per minute. Sintering temperatures lower than stated in the table may also be used subject to the peak temperature being maintained longer, for example, 1 to 2 hours. After the sintering, cooling may also be carried out more quickly, for example, even at a rate of approximately 20 C per minute. Finally it is stated that the sintering and also the subsequent cooling can also be carried out successfully in an oxygen atmosphere or in a mixture of air and oxygen. However, it is naturally simpler and easier to carry out the sintering in air.

TABLE A (Li Fees) and ZnO. M L M01 percent I I in a ratio varying from 0.25 l to 1.5 1 l, in which the 1 et 10.5 T T (o In. 8 1 a com No. Zn F0203 CH0 C00 (0 m (0 03 cm) lithium 1s present exclusively as 1 component ol 1 bivalent complex OXldC of a composmon according to g? ggg 81g 118g?) 3;? the formula (Li Fe., )O, and in which the iron .5 5 15. 99 198 225 00 L0 50.0 5.0 1,096 162 293 4'7 WhlCh 1s re ulred for thc formation of said b1 alcnt 1.0 50.0 15.0 1,040 174 1 complex oxlde is not included 1n the notation of the 3:? 28:3 i: quantity of iron, expressed in molecular percentages Fe O3, is compressed 1n the form of a magnetic core, b 5 5 1,083 155 230 L9 10 and the formed compressed core is sintered in air or a 0.5 51.0 10.0 1,083 260 221 2.8 0. 5 m 5 m 0 1,083 318 218 2. 7 mixture of air anod oxygen at a temperature wh1ch does 0.5 50.0 10.0 1,008 235 210 12 not exceed 1100 C.

I I c c 23 1:833 533 i3 2. A method as claimed 1n claim 1, characterized in 0.5 48.5 10. 0 1,050 317 102 24 a 5 48. 0 w. 0 1 050 361 185 31 that the starting mixture has a composmon of 0.5 17.5; 10. 1,025 333 180 20 15 46.550.5 mol %of Fe2O.-,, 0.5 ".1 11. 1.12. :1 :1 173 25 0. 5 1 7.0 10. 0 1,050 147 173 180 5 "101% Of C110. 0. 5 -l0. 0 10.0 0,! 1,000 340 180 22 0.5 40.0 10.0 1.0 1,000 1 20 1011 22 0 5 m0l OfCuQ, I 0.5 10. 0 10. 0 1.5 1. :12 I 7 22 rema1nder(L1M+ Fe0 )0 and Zn(),1n a ratio varying 0.5 40.0 10 2.5 1.000 1105 200 20 f ,0 l 0 75 l 0. 25 50.0 10 5.0 1,000 15 150 8 to 1 1 3. A method as claimed in claim I, characterized in 2) TABLE B '1" 142x10 M01 percent o-o t g] Lm/ '1. '10 (ohm. 1.x 5-28 23-55 Magnet core N0. Zn F0101 C110 C00 C.) 1.; 0.) cm) 10 C.

The following tables C and D relates to magnet cores in that the starting mixture has a composition of the manufacture of which the starting mixture was not 47.5 mOl 0f F6 0 prefired but was mixed with the binder after prolonged 35 5 15 mol% of CuO, grinding in a ball mill or a vibratory mill, and processes 0.7-2 mol Of COO, to a granulate, from which granulate rings were then remainder (Li0.5+Feo.5 )O a ,i Ii v rying compressed in the above-described manner, which from 0.25 l to l 1. rings were sintered in air, during which the peak tem- 4O 4. A method a claimed in claim 1, characterized in perature was again maintained for approximately l5 that at least one of the metal oxides composing the minutes. starting mixture is replaced by a compound of the same TABLE 0 metal, which is convertible into the corresponding M t l M 1 ercent Xmfi metal oxide during smterlng.

. 0 P 35 3 li p T. 8 (ohm. 45 5. A method as claimed in claim 1, characterized in F620 CH0 C00 m that the starting mixture is prefired at a temperature of 38 0.5 51.0 1.083 218 7 at most a roximat 1 950C cooled ulverized and 30 0.5 50.5 1,083 300 208 13 6 y p 40 0. 5 50.0 1,088 420 107 10 compressed 1n the form of a magnetic core. 41 0.5 9- 1.083 530 185 220 6. A soft-magnetic ferrite core consisting essentially 42 0.5 40.0 1,083 500 170 330 43 0, 5 4g 5 1,083 550 160 340 of a sintered reaction product of 44 0.5 48.0 1,083 500 140 340 5 45 0. 5 47. 5 1 083 540 135 32 mol Of F6203 5 20 mol of CuO,

TABLE 1) 0211x10 M01 purcent XltH '1. '18 (ohm. tgl ix 23- Magnet core No. LiM/Zn F0103 C110 C00 C.) 1; C cm.) 10" 23 C. C.

What is claimed is: 0- 5 mol of C00, and the remainder l. A method of manufacturing a soft-magnetic ferrite (Li +Fe0,5 )O and 200 in a ratio varying from 0.25: core,characterized in thatafinely divided starting mix- I to 1.5 l, the iron required for the formation of ture of iron oxide, F8 0 copper oxide, CuO, lithium (Li -i- Fe =f )0 not being included in the the quantity Oxide, Li O, zinc oxide, ZnO, and, Cobalt Oxide, COO, of iron, expressed in molecular percentages as Fe O having a composition expressed in molecular percentages of the metal oxides of 45.0- 52.55101 of F8103.

5 --20 mol of CuO,

0 5 mol of C00, and the remainder said core having an initial permeability (11.) higher than 150 at a temperature of 23C and a frequency of 4 kHz, a specific resistivity (p) at 23C higher than 10 ohmcm, and a Curie temperature higher than C.

mg UNITED STATES PATENT'OFFICE CERTIFICATE OF CORRECTION paten N 3,709,822 Dated January 9, 1973 Inventor(s) JOHANNES M.J. RITZIEN ET AL It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 13, -J should read -(I Column 2, line 20, "ZrO" should read -ZnO-;

I 3BA Column 2 lane 27, change 'Fe to read Fe a 3+ 3 Column 2, line 33, change "i Fe O5 to read Fe 5 Column 2, line 43, change "B153" to read --O Column 2, line 60, change "Fe20 to read F e 0 Column 3, line 8, change 'Zno" to read ZnO Column 4, line 5, change "Li (O to read Li CO Column 4, line 5, change "Co(0 to read -CoCO u Column 5, in TABLE B after "34" in "Magnet core No. column,

change "25" to read -35--;

Signed and sealed this 12th day of February 1974.

(SEAL) Attest:

EDWARD MFPLETCHER,JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents 

2. A method as claimed in claim 1, characterized in that the starting mixture has a composition of 46.5 - 50.5 mol % of Fe203, 5 - 20 mol % of Cu0, 0 - 2.5 mol % of Co0, remainder (Li0.5 + Fe0.53 )0 and Zn0, in a ratio varying from: 0.25 : 1 to 0.75 :
 1. 3. A method as claimed in claim 1, characterized in that the starting mixture has a composition of 47.5 - 50 mol % of Fe203 5 - 15 mol % of Cu0, 0.7 - 2 mol % of Co0, remainder (Li0.5 + Fe0.53 )0 and Zn0, in a ratio varying from 0.25 : 1 to 1 :
 1. 4. A method as claimed in claim 1, characterized in that at least one of the metal oxides composing the starting mixture is replaced by a compound of the same metal, which is convertible into the corresponding metal oxide during sintering.
 5. A method as claimed in claim 1, characterized in that the starting mixture is prefired at a temperature of at most approximately 950*C, cooled, pulverized and compressed in the form of a magnetic core.
 6. A soft-magnetic ferrite core consisting essentially of a sintered reaction product of 45 - 52.5 mol % of Fe203, 5 - 20 mol % of Cu0, 0 - 5 mol % of Co0, and the remainder (Li0.5 + Fe0.53 )O and Zn0 in a ratio varying from 0.25 : 1 to 1.5 : 1, the iron required for the formation of (Li0.5+ Fe0.53 )0 not being included in the the quantity of iron, expressed in molecular percentages as Fe2O3, said core having an initial permeability ( Mu ) higher than 150 at a temperature of 23*C and a frequency of 4 kHz, a specific resistivity ( Rho ) at 23*C higher than 106 ohm-cm, and a Curie temperature higher than 130*C. 